Any ideas of what this could possibly be?

Could it be somekind of tumor?

It could be a tumor but given the time of year it could also be a ectopic pregnancy where the fetus never attached in the womb and it is a fawn possibly growing outside the womb. In which case, it will kill her.

Blessings.....Pastorjim

bomiller: A couple of ideas: 1)a tumor as mentioned, 2)a rupture and if the doe is heavy in fawn with a rupture, the fawn may have dropped due to weaken muscles. Maybe show conservation the pictures and area where the pictures were taken. They could keep an eye out for her and check her out. Thanks for sharing.

Looks like it swallowed a basketball

it looks like a tumor or some sort of a rupture. littlearrow has a good idea, send the pics to conservation or contact your game warden and he can point you in the right direction.

yeah show this to dnr....

My wife (who's a doc, albeit a Radiologist) thinks it's a lipoma (fatty tumor). She said if you could hold her still, she could feel it and tell you.... But she said the doe appeared very health, so it is unlikely to be a cancer and she doubted it was related to a bad pregnancy.

coyotes haven't gotten her yet.

I slaughter hogs, i've seen this in many hogs before. All possibilities that you've gotten so for is a chance. In the hogs that i slaughter its a rupture of the abdominal wall and her intestines drop. From your photos that is given i see a young fawn with her, which leads me to assess this. During pregnancy she was able to give birth to a healthy one but then her inner wall was weak and the rupture happened. Sad part in the this is, if she happens to get pregnant again, chances are that neither one will make it. If she does she is very fortunate.